1. Field of the Invention
The invention relates to a printing machine roller, especially an ink roller, preferably for offset machines. In offset machines, continuous rollers with a surface coating are widely used as ink distributor cylinders.
2. Discussion of the Prior Art
In various fields of technical construction, there is a need for surfaces that can be easily moistened with oils, mineral oil, and substances bound with mineral oil, such as offset inks. Moreover, these surfaces must also be highly water-repellent (hydrophobic), because otherwise the ink film can be expected to break up, leading to what is known as blanking.
In offset printing machines, the inking unit is responsible for transferring the thinnest possible film of ink evenly onto the printing plate cylinder. In modern printing machines, the ink is transported via a complex roller system. Starting from an ink box, where the quantity of ink is controlled according to zone by ink blades that are positioned against an ink ductor roller, the ink is transported via a so called ink vibrator or lifter, or directly via an intermediate roller into the inking unit. The inking unit itself consists of several rollers, some of which continue to provide cross-distribution, which are responsible for supplying the necessary quantity of ink, in a defined manner, to the ink rollers in direct contact with the printing plate. In modern printing machines, because the rheological properties of the ink are of decisive importance in the printing process, some ink rollers are temperature-controlled. That is, an attempt is made to keep the ink temperature in a range that is favorable for the offset printing process. Only in this way is it possible to control the ink separating processes between two ink rollers. These ink separating processes are necessary to ensure that the supplied ink is divided as desired into ink to be transported farther and ink to be returned. According to the current state of the art, inking units are composed essentially of roller combinations that comprise a rubber roller and a polyamide roller. A widely known brand name for the polyamide coatings of the polyamide rollers is Rilsan. The Rilsan coatings, depending on their manufacture, are between 0.3 mm and 1.0 mm thick. This material has heat conductivity values in the range of 0.22 to 0.25 W/mK. Very low heat conductivity sharply limits the effectiveness of the internal temperature moderation (e.g., by means of temperature-moderated water) of the ink film on the roller.
Due to the heat insulation of the Rilsan layer, the vital information needed by the temperature control system, namely the ink film temperature, is usually transmitted to the temperature-moderating medium late and in dampened fashion. In other words, the control speed and control accuracy of this system are sharply limited.
Recently, this fact has become problematic not only in fast rotary machines, but also, specifically, in the water-free offset machines known as Toray machines. In fast rotary machines, due to the high dynamics, the heating of the ink film in the inking unit, triggered by the flexing and friction work of the roller pairs relative to one another, is extremely great, so that stable processes at high speeds are inconceivable without expensive internal cooling systems. Despite such constructive measures, however, inks must also be adjusted so as to have, like motor oil, a viscosity range useful in offset technology. If only special inks without such a broad viscosity range are used, massive ink separation problems occur in fast rotary machines, because the rheological properties of the ink are no longer suitable for offset printing. Such difficulties can include ink grabbing, inadequate ink density, an overall tendency to over-emulsification, ink shearing, etc.
In water-less offset machines (Toray), it is even more important to maintain a constant ink film temperature. The ink film must be kept at a temperature of 30.degree..+-.2.degree. C. This cannot be done satisfactorily at this time with Rilsan-coated ink distributors. Only very low web speeds are currently possible, particularly in rotary machines for implementing the Toray process. The output of these machines is thus sharply limited.